lhc searches for dark matter - university of oxford · evidence for dark matter galaxy rotation...
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LHC searches for dark matter
!
Uli Haisch
Evidence for dark matter
Galaxy rotation curves
Velocity
Radius
Observed
Disk
105 ly
/ 1pr
Gravitational lensing
Evidence for dark matter
X-ray image
Mass density contours
Bullet cluster
107 ly
Evidence for dark matter
Structure formation
109 ly
Content of Universe
Ordinary matter Dark matter Dark energy
But what is dark matter?
• As a particle physicist I want to know how dark matter (DM) fits into a particle description
• What do we know about it?
- Dark (neutral)
- Massive
- Still around today (stable or with a lifetime exceeding the age of the Universe)
• Nothing in the Standard Model of particle physics fits the profile
Standard Model (SM)
Mass: _______
Spin: _______
Lifetime: _______
Couplings:
Gravity
Weak interaction?
Higgs?
Quarks/gluons?
Leptons?
Thermal relic?
Yes No
DM questionnaire
Particle probes of DM
• The common theme of searches for DM is that all methods are determined by how the DM particles interact with the SM
Fermi telescope
χ
χ
SM particlesDM particles
Indirect detection
Particle probes of DMLUX detector
χ χ
SM particles
DM particles
Direct detection
• The common theme of searches for DM is that all methods are determined by how the DM particles interact with the SM
Particle probes of DM
χ
χ
SM particles DM particles
Collider searches
• The common theme of searches for DM is that all methods are determined by how the DM particles interact with the SM
LHC at CERN
CDMS II
Has DM already been seen?
19
Energy (GeV)
Eve
nts
/ 5.0
GeV
0
10
20
30
40
50
60
70 = 130.0 GeVγP7CLEAN R3 1D E = 24.8 evtssign
σ = 4.5 locals
= 298.2 evtsbkgn
= 2.78bkgΓ
(a)
Energy (GeV)40 60 80 100 120 140 160 180 200 220
)σ
Res
id. (
-4-2024
Energy (GeV)
Eve
nts
/ 5.0
GeV
0
10
20
30
40
50
60
70 = 133.0 GeVγ
P7_REP_CLEAN R3 1D E = 21.2 evtssign
σ = 4.1 locals
= 272.8 evtsbkgn
= 2.82bkgΓ
(b)
Energy (GeV)60 80 100 120 140 160 180 200 220
)σ
Res
id. (
-4-2024
Energy (GeV)
Eve
nts
/ 5.0
GeV
0
10
20
30
40
50
60
70 = 133.0 GeVγ
P7_REP_CLEAN R3 2D E = 17.8 evtssign
σ = 3.3 locals
= 276.2 evtsbkgn
= 2.76bkgΓ
(c)
Energy (GeV)60 80 100 120 140 160 180 200 220
)σ
Res
id. (
-4-2024
FIG. 12. Fits for a line near 130 GeV in R3: (a) at 130 GeV in the P7CLEAN data using the 1D energy dispersion model(see Sec. IV); (b) at 133 GeV in the P7REP CLEAN data again using the 1D model; (c) same as (b), but using the 2D energydispersion model (see Sec. IV). The solid curve shows the average model weighted using the PE distribution of the fitted events.Note that these fits were unbinned; the binning here is for visualization purposes, and also that the x-axis binning in (a) iso↵set by 3 GeV relative to (b) and (c).
Fermi-LAT
DM?
DM?
• Claims for DM discovery have been made based on the results of indirect and direct detection experiments. Since the backgrounds in both cases are large and uncertain (and given that we have no control over the signal), claims remain unsubstantiated
ATLAS detector
46 m ✕ 25 m, 7000 t, 3000 km of cables, …
DM production at the LHC
• If DM particles are sufficiently light and couple to quarks or gluons, we should be able to produce them at the LHC
• By studying DM production in proton-proton collisions, we are testing the inverse of the process that kept DM in thermal equilibrium in the early Universe
• LHC may allow us to produce other states of “dark sector”, which are no longer present in the Universe today
How to see the invisible?• The DM particles interact so weakly that they are expected to pass out
of the detector components without any significant interaction, making them effectively invisible (much like neutrinos)
χ
χ
SM particles
Visible radiation
Missing momentum
• One way to “see” DM particles nonetheless, works by looking for “missing momentum” and additional SM radiation
How to see the invisible?
How to see the invisible?
Missing momentum Missing
momentum
How to see the invisible?
χχSM particles
SM particle
“Partner” particles
Missing momentum
SM particle
• Second way to try to detect SM, based on production of “partner” particles that decay to DM and SM particles
“Bump hunting” for the Higgs
The di-photon decay of the
Higgs leads to a nice bump in the invariant mass distribution
“Bump hunting” for the Higgs
To see the bump for the Higgs
decaying to two Z bosons, one does not even
have to zoom in
“Tail surgery” to find DM
200 400 600 800 1000 12000
2000
4000
6000
8000
10000
ET , miss [GeV]
dN/dE T,miss[events/GeV
]SM background
DM signal
Overwhelming SM background, that arises in the case of mono-
jet searches from Z + jet production with the Z boson
decaying to neutrinos
“Tail surgery” to find DM
SM background
DM signal
The presence of DM manifests itself in a small enhancement in the tail of the missing energy
distribution
SM background
DM signal
200 400 600 800 1000 120010-2
0.1
1
10
100
1000
104
ET , miss [GeV]
dN/dE T,miss[events/GeV
]
A big challenge indeed
Experimentalist
How well can I calculate these small numbers?
Theorist
How well can I measure the few events sitting in
the tail?
Proton
Parton distribution functions
Precision QCD predictions
Z
Precision QCD predictions
Proton
Parton distribution functions
Neutrino
Gluon
Hard scattering process
Neutrino
Z
Precision QCD predictions
Proton
Parton distribution functions
Hard scattering process
Neutrino
Gluon
Neutrino
Parton shower evolution
Z
Precision QCD predictions
Proton
Parton distribution functions
Hard scattering process
Neutrino Neutrino
Parton shower evolution
Gluon
Clustering, hadronisation and decays
Pions, leptons and photons
But we also need a DM theory
• The three main search strategies perform quite different measurements. Without a theoretical model of DM, we cannot compare the results
• If evidence for DM is found in one type of search, we can predict in a given model the signals that should be seen in other searches
χDirect detection Indirect detection
Collider searches
No lack of theoretical models
mSUGRA
R-parityConserving
Supersymmetry
pMSSM
R-parityviolating
Gravitino DM
MSSM NMSSM
DiracDM
Extra Dimensions
UED DM
Warped Extra Dimensions
Little Higgs
T-odd DM
5d
6d
Axion-like Particles
QCD Axions
Axion DM
Sterile Neutrinos
LightForce Carriers
Dark Photon
Asymmetric DM
RS DM
Warm DM
?
HiddenSector DM
WIMPless DM
Littlest Higgs
Self-InteractingDM
Q-balls
T Tait
Solitonic DM
QuarkNuggets
Techni-baryons
Dynamical DM
Theories of Dark Matter
mSUGRA
R-parityConserving
Supersymmetry
pMSSM
R-parityviolating
Gravitino DM
MSSM NMSSM
DiracDM
Extra Dimensions
UED DM
Warped Extra Dimensions
Little Higgs
T-odd DM
5d
6d
Axion-like Particles
QCD Axions
Axion DM
Sterile Neutrinos
LightForce Carriers
Dark Photon
Asymmetric DM
RS DM
Warm DM
?
HiddenSector DM
WIMPless DM
Littlest Higgs
Self-InteractingDM
Q-balls
T Tait
Solitonic DM
QuarkNuggets
Techni-baryons
Dynamical DM
Theories of Dark Matter
No lack of theoretical models
Less complete
More complete
Spectrum of DM theory space
Complete models
Effective field theories
Simplified models
Minimal supersymmetric
SM
Universal extra
dimensionsLittle Higgs
Higgs portal
Z′ boson
Squarks
Contact Interactions
Models
Sketches of models
Dark photon
Dipole interactions
Complete DM theories
Complete = complicated
Minimal supersymmetric SM (MSSM)
ct
d
s
b
eμ νi
u
τ
Z
γ
W
H
g∼
∼∼
∼
∼
∼
∼
∼
∼∼
∼∼
∼
∼
∼
• All complete DM models add more particles to the SM, most of which are not viable DM candidates
• The classical example is the MSSM, in which each SM particle gets its own “superpartner”
• In the case of the MSSM there are 20 additional parameters that can be relevant for DM physics
One way to produce DM in MSSM
χ
χ
Top quark
Top quarkTop
squarkProton
Gluon
LHC limits on DM mass in MSSM
250 GeV
LHC limits on DM mass in MSSM
Range of DM masses unexplored
by the first LHC run
250 GeV
Range of DM masses unexplored
by the first LHC run
175 GeV
Masses of all the SM particles: top quark, Higgs, Z boson, …
LHC limits on DM mass in MSSM
LHC limits on DM mass in MSSM
Ultimate reach of the LHC
250 GeV
Excluded by the first LHC run
600 GeV
DM effective field theories
Effective = easy
• At the other end of complexity are models in which the DM particles are the only new states that can be produced at the LHC
• In such cases, effective field theory allows us to describe the DM-SM interactions mediated by all heavy particles in a simple and universal way
χ1 GeV
5 TeV
Mass
Z3
Z2Z1
Very heavy states with DM-SM interactions
q
p = pq̄ + pq = pX̄ + pX
=q̄
q
X̄
XZ1 g2
p2 �M2Z1
(q̄�q)(X̄�X)
Effective field theory primer
p = pq̄ + pq = pX̄ + pX p2 ⌧ M2Z1
=q̄
q
X̄
XZ1 g2
p2 �M2Z1
(q̄�q)(X̄�X)
� g2
M2Z1
(q̄�q)(X̄�X)
Effective field theory primer
� g2
M2Z1
(q̄�q)(X̄�X)� 1
M2⇤
Effective field theory primer
=
=
q̄
q
X̄
XZ1
p2 ⌧ M2Z1
X̄
Xq
q̄
g2
p2 �M2Z1
(q̄�q)(X̄�X)
1
M2⇤=
g2
M2Z1
X̄
Xq
q̄
Independent of heavy physics
Information on heavy states encoded in a single coupling
χ1 GeV
5 TeV
Mass
Z3
Z2Z1
q
Effective field theory primer
LHC limits on suppression scale
[GeV]χWIMP mass m
210 310
[GeV
]*
Sup
pres
sion
sca
le M
200
400
600
800
1000
1200
, SR3, 90%CLOperator D5
)expσ 2± 1 ±Expected limit (
)theoryσ 1±Observed limit (
Thermal relic
PreliminaryATLAS
=8 TeVs-1
Ldt = 10.5 fb∫
not valideffective theory
700 GeV
Excluded by the first LHC run
Direct detection excluded
Comparison with direct detection
The LHC constraints are strongest at low DM mass, where direct detection is challenging due to the small nuclear recoil
LHC excluded
Spin-independent interactions
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Spin-dependent interactions
LHC excluded
Direct detection excluded
The LHC is superior to any spin-dependent search for all DM masses, since DM-nucleon scattering is incoherent in this case
Comparison with direct detection
Simplified DM models
Simplified = in-between
Z2Z3
χ1 GeV
5 TeV
Mass
Z1
q
State with DM-SM interactions that can be produced at the LHC
• Another interesting option is to consider models that contain DM and the most important state mediating its interactions with the SM
• Unlike the effective field theories, these simplified models can describe the full kinematics of DM production at the LHC
• Simplified DM models have typically a few parameters
Outlook
• Dark matter implies physics beyond the Standard Model
• An understanding of dark matter thus requires new theoretical concepts. These can be complete models, but it is also fruitful to think about less defined, more hazy sketches of theories
• Searches at the LHC, in underground experiments and in astrophysical observations naturally target different parts of the dark matter theory space. They complement one another
• Once we have a detection, only the full suite of techniques will allow us to fully learn what dark matter really is
The LHC can bring sketches of dark matter to life!
A possible timeline
Mass
Spin
Stable?
Couplings:
Gravity
Weak interaction?
Higgs?
Quarks/gluons?
Leptons?
Thermal relic?
2013
2014
2015
2016
2017
2018
LUX sees a handful of elastic scattering events consistent with a DM mass < 200 GeV
Mass: < 200 GeV
Spin
Stable?
Couplings:
Gravity
Weak interaction?
Higgs?
Quarks/gluons
Leptons?
Thermal relic?
?
A possible timeline2013
2014
2015
2016
2017
2018
LUX sees a handful of elastic scattering events consistent with a DM mass < 200 GeV Fermi observes a faint gamma
ray line at 150 GeV from the galactic center
Mass: 150 +/- 15 GeV
Spin
Stable?
Couplings:
Gravity
Weak Interaction?
Higgs?
Quarks/gluons
Leptons?
Thermal Relic?
2013
2014
2015
2016
2017
2018
A possible timeline
Fermi observes a faint gamma ray line at 150 GeV from the
galactic center
Two LHC experiments see a significant excess of leptons
plus missing energy
Mass: 150 +/- 15 GeV
Spin
Stable?
Couplings:
Gravity
Weak interaction?
Higgs?
Quarks/gluons
Leptons?
Thermal relic?
?
?
Xenon sees a similar signal
2013
2014
2015
2016
2017
2018
A possible timeline
LUX sees a handful of elastic scattering events consistent with a DM mass < 200 GeV
Xenon sees a similar signal
2013
2014
2015
2016
2017
2018
Neutrinos are seen coming from the
Sun by IceCubeNo jets
plus missing energy
Mass: 150 +/- 15 GeV
Spin: > 0
Stable?
Couplings:
Gravity
Weak interaction
Higgs?
Quarks/gluons
Leptons
Thermal relic?
X
A possible timeline
Fermi observes a faint gamma ray line at 150 GeV from the
galactic center
Two LHC experiments see a significant excess of leptons
plus missing energy
Neutrinos are seen coming from the
Sun by IceCube.
A positive signal of axion conversion is observed at an
upgraded ADMX
A possible timeline2013
2014
2015
2016
2017
2018
Fermi observes a faint gamma ray line at 150 GeV from the
galactic center
Two LHC experiments see a significant excess of leptons
plus missing energyXenon sees
a similar signal
LUX sees a handful of elastic scattering events consistent with a DM mass < 200 GeV
Mass: 150 +/- 15 GeV
Spin: > 0
Stable?
Couplings:
Gravity
Weak interaction
Higgs?
Quarks/gluons
Leptons
Thermal relic?
X
Mass: 20 μeV
Spin: 0
Stable
Couplings:
Gravity
Photon interaction
Higgs?
Quarks/gluons?
Leptons?
Thermal relic?X
X
LUX sees a handful of elastic scattering events consistent with a DM mass < 200 GeV.
Xenon sees a similar signal.
Two LHC experiments see a significant excess of leptons
plus missing energy.
No jets + MET
A positive signal of axion conversion is observed at an
upgraded ADMX
Observation at a Higgs factory indicates that the interaction with leptons is too strong to saturate the
relic density????
Mass: 150 +/- 0.1 GeV
Spin: > 0
Stable?
Couplings:
Gravity
Weak unteraction
Higgs?
Quarks/gluons
Leptons
Thermal relic
X
Mass: 20 μeV
Spin: 0
Stable
Couplings:
Gravity
Photon interaction
Higgs?
Quarks/gluons?
Leptons?
Thermal relicX
X
A possible timeline2013
2014
2015
2016
2017
2018
Neutrinos are seen coming from the
Sun by IceCube
Fermi observes a faint gamma ray line at 150 GeV from the
galactic center
Neutrinos are seen coming from the
Sun by IceCube
Fermi observes a faint gamma ray line at 150 GeV from the
galactic center
LUX sees a handful of elastic scattering events consistent with a DM mass < 200 GeV.
Xenon sees a similar signal.
Two LHC experiments see a significant excess of leptons
plus missing energy.
No jets + MET
A positive signal of axion conversion is observed at an
upgraded ADMX
Observation at a Higgs factory indicates that the interaction with leptons is too strong to saturate the
relic density????
Mass: 150 +/- 0.1 GeV
Spin: > 0
Stable?
Couplings:
Gravity
Weak interaction
Higgs?
Quarks/gluons
Leptons
Thermal relic
X
Mass: 20 μeV
Spin: 0
Stable
Couplings:
Gravity
Weak interaction
Higgs?
Quarks/gluons?
Leptons?
Thermal relicX
A multi-pronged search strategy identifies a mixture of dark matter which is 50% weakly interacting particle and 50% axion
X
A possible timeline2013
2014
2015
2016
2017
2018